Multi-channel stereo reproducing apparatus

ABSTRACT

The present invention provides a multi-channel stereo reproducing apparatus which can reproduce a recording medium such as an audio disc or the like in which in order that users can enjoy screen musics or the like reproduced at, for example, a concert hall and a movie theater. In the de-emphasis circuit is by-passed, whereby, when reproducing a recording medium on which a multi-channel stereo signal in which the high frequency component of the rear signal B is pre-emphasized is recorded, a high frequency component of a delayed difference signal t (L-R) supplied to the rear loudspeaker is de-emphasized so as to make the total frequency characteristic relative to the rear signal B flat, while when reproducing the recording medium on which the 2-channel stereo signal formed of only the left and right front signals L and R in which the center front signal F and the rear signal B are not encoded at all is recorded, the de-emphasis circuit is by-passed so as to prevent the delayed difference signal t (L-R) supplied to the rear loudspeaker from being attenuated to thereby, in either cases, present satisfactory stereo presence.

TECHNICAL FIELD

The present invention relates to multi-channel stereo reproducingapparatus and particularly to a multi-channel stereo reproducingapparatus which can selectively reproduce a recording medium such as avideo disc or the like (a so-called Dolby surround-phonic sound systemstereo) on which a multi-channel stereo signal is recorded such that ahigh frequency component of its rear signal is pre-emphasized forlisteners to enjoy screen music reproduced at a concert hall and a movietheater, and a recording medium on which a standard 2-channel stereosignal is recorded.

BACKGROUND ART

When a motion picture is shown at a concert hall and a movie theater, anaudio signal is generally reproduced by means of Dolby surround-phonicsound system 4-channel stereo reproducing system to urge audiences tofeel as if they were in the very place shown on the picture screen.

When a motion picture for a movie theater is produced, a video signal isrecorded and at the same time, left front sound, right front sound,center front sound and rear sound are recorded respectively. In thiscase, a left front signal L_(F), a right front signal R_(F), a centerfront signal F and a rear signal B are encoded respectively and thenrecorded on a video disc or a magnetic tape as LT and RT signals,respectively. In this case, in order to improve a signal-to-noise ratio,or a so-called S/N ratio of the rear signal B, there is employed aso-called modified B-type Dolby system in which a high frequencycomponent higher than 1 kHz is emphasized (pre-emphasis) by apredetermined amount and then recorded. FIG. 3 illustrates frequency vs.response characteristics in the case where the recording level is at 0dB, -10 dB, -20 dB and -30 dB in this modified B-type Dolby system.Then, the left front signal L_(F), the right front signal R_(F), thecenter front signal F and the rear signal B thus recorded are furtherencoded to a left composite signal L_(T) and a right composite signalR_(T) which are respectively expressed as L_(T) =L_(F) +(F/2+2) andR_(T) =R_(F) +(F/2)-(B/2). These left and right composite signals L_(T)and R_(T) are optically recorded, in the case of, for example, a 35 mmfilm, at a sound track portion located at a predetermined position ofthe film according to the brightness change system which carries out therecording on the basis of the change of light and shade of, for example,the coloring. Accordingly, when a motion picture is shown, the left andright composite signals L_(T) and R_(T) thus optically recorded aredecoded so as to produce four signals of the left composite signalL_(T), the right composite signal R_(T), a sum signal L_(T) +R_(T) ofthe left composite signal L_(T) and the right composite signal R_(T) anda difference signal L_(T) -R_(T) of the left composite signal L_(T) andthe right composite signal R_(T). Then, these four signals arereproduced by a left front loudspeaker, a right front loudspeaker, acenter front loudspeaker and a rear loudspeaker. In this case, since thehigh frequency component of the rear signal B is pre-emphasized by themodified B-type Dolby system as described hereinabove, upon reproducing,the high frequency component of the difference signal L_(T) -R_(T) isattenuated (de-emphasized) so as to make a total frequencycharacteristic flat relative to the rear signal B. When the audio signalis reproduced by such 4-channel stereo reproducing system, the soundeffect is enhanced to provide presence so that the listeners are urgedto feel as if they were in the very place shown on the picture screen.

By the way, a magnetic tape and a video disc by which the user can enjoythe screen music recorded thereon for the motion picture or the mortionpicture itself are now available on the market. In this case, since therecorded signals recorded on the magnetic tape and the video disc arethe composite signals L_(T) and R_(T) as described hereinabove, there isproposed a multi-channel stereo reproducing apparatus illustrated inFIG. 1.

In FIG. 1, reference numerals 1 and 2 respectively designate left andright composite signal input terminals to which the left and rightcomposite signals L_(T) and R_(T) are supplied. The respective left andright composite signal input terminals 1 and 2 are connected to theinput side of a balancing circuit 3, and the balancing circuit 3produces at its output sides left and right composite signals L_(T) andR_(T) which are so balanced as to localize an acoustic image normally.

The output sides of the balancing circuit 3 are connected throughamplifiers 4 and 5 to left and right front loudspeakers 6 and 7 whichrespectively reproduce the left and right composite signals L_(T) andR_(T) supplied to the left and right composite signal input terminals 1and 2.

Also, the output sides of the balancing circuit 3 are connected to theinput side of a mixing circuit 8 which generates at its output side thesum signal L_(T) +R_(T) of the left and right composite signals L_(T)and R_(T). The output side of the mixing circuit 8 is connected throughan amplifying circuit 9 to a center front loudspeaker 10 whichreproduces the sum signal L_(T) +R_(T) developed at the output side ofthe mixing circuit 8.

Further, the output sides of the balancing circuit 3 are connected tothe input sides of a subtracting circuit 11 and the subtracting circuit11 generates at its output side the left and right composite signalsL_(T) and R_(T) of which the monaural components are removed. The outputside of the subtracting circuit 11 is connected to the input side of adelay circuit 12, and the delay circuit 12 generates at its output sidea delayed difference signal Δt (L_(T) -R_(T)) which is delayed by apredetermined delay time. Thus, a front localization feeling and awidening feeling of sound field are obtained. The output side of thedelay circuit 12 is connected to the input side of a filter for passingtherethrough a signal of low frequency band, that is, so-called low passfilter 13, and the low pass filter 13 generates at its output side thedelayed difference signal Δt (L_(T) -R_(T)) in which a clock pulsecomponent given by the passing of the signal through the delay circuit12 and the like are removed and the high frequency component higher thana predetermined frequency is removed so as to balance the low frequencycomponent which is not sufficient in the difference signal L_(T) -R_(T).The output side of the low pass filter 13 is connected to the input sideof a de-emphasis circuit 14 which attenuates the high frequencycomponent of the delayed difference signal Δt (L_(T) -R_(T)) higher than1 kHz, thus producing a delayed difference signal Δt (L_(T) -R_(T)) inwhich the total frequency characteristic of the rear ? signal B of whichthe high frequency component higher than 1 kHz is emphasized in responseto the response thereof is made flat. Then, the output side of thede-emphasis circuit 14 is connected through amplifying circuits 15 and16 to left and right rear loudspeakers 17 and 18 by which the delayeddifference signal Δt (L_(T) -R_(T)) in which the T frequencycharacteristic of the rear signal B is made flat, is reproduced.

In the conventional multi-channel stereo reproducing apparatus thusconstructed, the left and right composite signals L_(T) and R_(T) arereproduced from the left and right front loudspeakers 6 and 7, the sumsignal L_(T) +R_(T) is reproduced from the center front loudspeaker 10and the delayed difference signal Δt (L_(T) -R_(T)) is reproduced fromthe left and right rear loudspeakers 17 and 18.

Consequently, according to such known multi-channel stereo reproducingapparatus, the sound effect is enhanced to produce good stereo presencethe same as that in the concert hall.

However, by such conventional multi-channel stereo reproducingapparatus, when reproducing a recording medium, such as, a record disk,a cassette tape and so on available on the market and on which thestandard 2-channel stereo signal formed of the left front signal L_(F)and the right front signal R_(F) in which the center front signal F andthe rear signal B are not encoded at all are recorded, since the delayeddifference signal Δt (L_(F) -R_(F)) from the delay circuit 12 passesthrough the de-emphasis circuit 14, its high frequency component higherthan 1 kHz is attenuated. Then, the delayed difference signal Δt (L_(F)-R_(F)) of which the high frequency component is attenuated isreproduced from the left and right rear loudspeakers 17 and 18, so thatthe high frequency component of the sound reproduced by the rearloudspeakers is attenuated unnaturally. Thus, satisfactory stereopresence can not be obtained.

DISCLOSURE OF INVENTION

In view of such aspects, the present invention is to provide amulti-channel stereo reproducing apparatus which can selectivelyreproduce a recording medium on which a multi-channel stereo signal inwhich the high frequency component of the rear signal is pre-emphasizedis recorded and a recording medium on which a standard 2-channel stereosignal is recorded.

According to the present invention, in a multi-channel stereoreproducing apparatus which is so arranged as to reproduce a recordingmedium in which if a left front signal is taken as L_(F), a right frontsignal is taken as R_(F), a center front signal is taken as F and a rearsignal is taken as B, these signals are encoded to left and rightcomposite (signals L_(T) and R_(T) expressed as L_(T) =L_(F) F/2)+(B/2)and R_(T) =R_(F) +(F/2)-(B/2,) the high frequency component of the rearsignal B is pre-emphasized and then they are recorded, this apparatus isprovided with a matrix circuit for producing a left composite signalL_(T), a right composite signal R_(T), a sum signal L_(T) +R_(T) of theleft composite signal L_(T) and the right composite signal R_(T) and adifference signal L_(T) -R_(T) of the left composite signal L_(T) andthe right composite signal R_(T), a reproducing circuit for reproducingthe left composite signal L_(T), the right composite signal R_(T) andthe sum signal L_(T) +R_(T) and a reproducing circuit for reproducingthe difference signal L_(T) -R_(T) through a delay circuit and ade-emphasis circuit, wherein when reproducing a recording medium inwhich the 2-channel stereo signal formed of only the left and rightfront signals L_(F) and R_(F) in which the center front signal F and therear signal B are not encoded at all is recorded, the de-emphasiscircuit can be by-passed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing an example of a conventionalmulti-channel stereo reproducing apparatus,

FIG. 2 is a block diagram showing an embodiment of a multi-channelstereo reproducing apparatus according to the present invention and

FIG. 3 is a graph used o explain the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of a multi-channel stereo reproducing apparatus accordingto the present invention will hereinafter be described with reference toFIG. 2. In FIG. 2, like parts corresponding to those of FIG. 1 aremarked with the same references and will not be described in detail.

In accordance with this embodiment, the output side of the low passfilter 13 is connected to the input side of the de-emphasis circuit 14and to one fixed contact 19a of a change-over switch 19. In this case,the de-emphasis circuit 14 is adapted to de-emphasize the high frequencycomponent of the audio signal pre-emphasized by the modified B-typeDolby system to thereby make the total frequency characteristic flat.

The output side of the de-emphasis circuit 14 is connected to the otherfixed contact 19b of the change-over switch 19 and a movable contact 19cof the change-over switch 19 is connected through the amplifyingcircuits 15 and 16 to the left and right rear loudspeakers 17 and 18,whereby the de-emphasis circuit 14 can be by-passed, if necessary. Otherarrangements are formed the same as those of the prior art shown in FIG.2.

In the thus constructed multi-channel stereo reproducing apparatus ofthis embodiment, when the movable contact 19c of the change-over switch19 is connected to the other fixed contact 19b, the circuit arrangementis formed the same as that of the example of the prior art in FIG. 2.Accordingly, the left front signal L_(F), the right front signal R_(F),the center front signal F and the rear signal B are encoded respectivelyto the left and right composite signals L_(T) and R_(T) which arerespectively expressed as L_(T) =L_(F) +(F/2)+(B/2) and R_(T) =R_(F)+(F/2)-(B/2). At the same time, when reproducing a recording medium onwhich a high frequency component of the rear signal B higher than 1 kHzis pre-emphasized by the modified B-type Dolby system and recorded, forexample, a video disc or the like on which screen music or the likerecorded for the motion picture is recorded, the left composite signalL_(T) =L_(F) +(F/2)+(B/2) is reproduced from the left front loudspeaker6, the right composite signal R_(T) =R_(F) +(F/2)-(B/2) is reproducedfrom the right front loudspeaker 7, the sum signal L_(T) +R_(T) =L_(F)+R_(F) +F of the left composite signal L_(T) and the right compositesignal R_(T) is reproduced from the center front loudspeaker 10 and thedelayed difference signal Δt (L_(T) -R_(T))=Δt (L_(F) -R_(F) +B) isreproduced from the left and right rear loudspeakers 17 and 18. In thiscase, since 5 the delayed difference signal Δt (L_(T) -R_(T))=Δt (L_(F)-R_(F) +B) is reproduced in such a manner that its high frequencycomponent is attenuated by the de-emphasis circuit 14 and that its totalfrequency characteristic relative to the rear signal B is made flat, thesound effect can be enhanced to produce stereo presence the same as thatobtained in the concert hall and the movie theater.

According to the multi-channel stereo reproducing apparatus of thisembodiment, it is possible to reproduce the standard 2-channel stereosignal formed of the left and right front signals L_(F) and R_(F) inwhich the center front signal F and the rear signal B are not encoded atall. In this case, when the left and right front signals L_(F) and R_(F)are supplied to the left and right composite signal input terminals 1and 2, the left and right front signals L_(F) and R_(F) are reproducedfrom the left and right loudspeakers 6 and 7, the sum signal L_(F)+R_(F) of the left front signal L_(F) and the right front signal R_(F)is reproduced from the center front loudspeaker 10 and the delayeddifference signal Δt (L_(F) -R_(F)) which results from delaying thedifference signal L_(F) -R_(F) of the left front signal L_(F) and theright front signal R_(F) by a predetermined delay time is reproducedfrom the rear loudspeakers 17 and 18. In addition, according to thisembodiment, since the movable contact 19c of the change-over switch 19is connected to one fixed contact 19a to by-pass the de-emphasis circuit14 to thereby directly connect the output side of the low pass filter 13to the amplifying circuits 15 and 16, without attenuating the highfrequency component of the delayed difference signal Δt (L_(F) -R_(F))obtained at the output side of the low pass filter 13, this delayeddifference signal At (L_(F) -R_(F)) can be reproduced. When the delayeddifference signal Δt (L_(F) -R_(F)) is reproduced together with the leftfront signal L_(F), the right front signal R_(F) and the sum signalL_(F) +R_(F), it is well known that stereo presence can be increased andhence the atmosphere as presented at the concert hall and the movietheater can be obtained.

Consequently, according to this embodiment, it is possible toselectively reproduce the recording medium in which the left frontsignal L_(F), the right front signal R_(F), the center front signal Fand the rear signal B are encoded respectively to the left and rightcomposite signals L_(T) and R_(T) expressed as L_(T) =L_(F) +(F/2) (B/2)and R_(T) =R_(F) +(F/2)-(B/2) and the high frequency component of therear signal B is pre-emphasized by the modified B-type Dolby system andthe recording medium for the standard 2-channel stereo signal formed ofthe left and right front signals L_(F) and R_(F) in which the centerfront signal F and the rear signal B are not encoded at all. In eithercases, it is possible to obtain the stereo presence the same as thatobtained at the concert hall and the movie theater.

While in the above embodiment, the present invention is applied to themulti-channel stereo reproducing apparatus for reproducing a recordingmedium on which the multi-channel stereo signal in which the rear signalB is pre-emphasized by the modified B-type Dolby system is recorded asdescribed hereinabove, the present invention is not limited to the abovementioned embodiment but can be applied to a multi-channel stereoreproducing apparatus for reproducing a recording medium on which asignal pre-emphasized by other noise reduction system is recorded orsuch an apparatus in which the above delay circuit is formed of adigital circuit having an A/D converter and a D/A converter. It caneasily be understood that the same action and effect as described abovecan be achieved also in this case.

It is needless to say that the present invention is not limited to theafore-mentioned embodiment but can take various modifications withoutdeparting from the gist of the present invention.

I claim:
 1. In a multi-channel stereo reproducing apparatus forreproducing a recording medium on which if a left front signal is takenas L_(F), a right front signal is taken as R_(F), a center front signalis taken as F and a rear signal is taken as B, these signals are encodedto left and right composite signals L_(T) and R_(T) respectivelyexpressed as L_(T) =L_(F) +(F/2)+(B/2) and R_(T) =R_(F) +(F/2)-(B/2),the high frequency component of said rear signal B is pre-emphasized andthen they are recorded, said multi-channel stereo reproducing apparatusbeing characterized in that there are provided a matrix circuit forproducing said left composite signal L_(T), said right composite signalR_(T), a sum signal L_(T) +R_(T) of said left composite signal L_(T) andsaid right composite signal R_(T) and a difference signal L_(T) -R_(T)of said left composite signal L_(T) and said right composite signalR_(T), reproducing circuit for reproducing said left composite signalL_(T), said right composite signal R_(T) and said sum signal L_(T)+R_(T) and a reproducing circuit for reproducing said difference signalL_(T) -R_(T) through a delay circuit and a de-emphasis circuit, whereinthe improvement is provided means for by-passing said de-emphasiscircuit when reproducing a recording medium on which a 2-channel stereosignal formed of only said left and right front signals L_(F) and R_(F)is recorded in which the center front signal F and the rear signal B arenot encoded at all is recorded so that the high frequency component ofthe sound reproduced by the rear loudspeakers is alternated unnaturally.2. A multi-channel stereo reproducing apparatus according to claim 1,wherein said by-pass means is formed of a change-over switch having apair of fixed contacts and a movable contact, said pair of fixedcontacts being respectively connected to the input and output sides ofsaid de-emphasis circuit, and said movable contact being connected tothe output side of said reproducing circuit.
 3. A multi-channel stereoreproducing apparatus according to claim 2, wherein said de-emphasiscircuit is given a frequency characteristic in which a signal level of ahigh frequency is emphasized in response to a signal level of saiddifference signal L_(T) -R_(T).
 4. A multi-channel stereo reproducingapparatus according to claim 3, wherein said frequency characteristic issuch one that when the signal level is about 30 dB, a signal level of asignal higher than about 4 kHz is emphasized by 5 dB.